Pavement markers are conventionally applied to road pavement surfaces by means of a suitable adhesive. Various adhesive dispensing mechanisms are conventionally mounted upon a road vehicle that moves along a road pavement surface upon which the pavement markers are to be applied. The adhesive material is dispensed onto a predetermined location of the road pavement surface by means of the particular adhesive dispensing mechanism or apparatus, and subsequently, a technician/operator, riding upon the road vehicle at a position directly behind the dispensing mechanism or apparatus, or another mechanism of the dispensing apparatus located upon the vehicle at a position directly behind the dispensing mechanism or apparatus, applies a pavement marker to the freshly deposited adhesive. When the adhesive cures, the pavement marker is fixedly secured or bonded to the road pavement surface.
Various valve mechanisms or adhesive applicators, utilized in conjunction with pavement marker application machines, or for other purposes, are of course well known such as, for example, U.S. Pat. No. 4,887,741 which issued to Downing on Dec. 19, 1989, U.S. Pat. No. 5,888,018 which issued to Green on Mar. 30, 1999, U.S. Pat. No. 5,934,822 which issued to Green on Aug. 10, 1999, United States Patent Application Publication 2002/0139818 which was published on Oct. 3, 2002 for McGuffey, U.S. Pat. No. 7,614,529 which issued to Bolyard, Jr. et al. on Nov. 10, 2009, United States Patent Application Publication 2013/0334252 which was published on Dec. 19, 2013 for Dorman et al., and U.S. Pat. No. 8,746,501 which issued to Saine on Jun. 10, 2014.
In order for an adhesive dispensing valve to be suitable for the deposition of adhesive material onto a pavement road surface so as to successfully facilitate the fixation of a pavement marker to the pavement road surface, the adhesive dispensing valve must satisfy several important operating criteria. For example, the valve needs to effectively provide the adhesive deposition with a consistent shape and thickness, such as, for example, a substantially square deposit of material of approximately four and one-half inches per side to which, for example, a four-inch square pavement marker can be adhered, and with a thickness of approximately one-eighth to one-quarter of an inch, although the particular thickness will vary depending upon the type and coarseness of the road surface to which the markers are being applied. Along these lines, it is to be noted that rough chip seal roads require a thicker deposit of adhesive than smooth concrete.
In addition, the valve needs to dispense the adhesive material extremely quickly. The faster the valve can dispense the required amount of adhesive, the faster the road vehicle carrying the adhesive applicator apparatus can travel down the road, the greater the distance that can be covered within a predetermined time frame, the greater the number of pavement markers that can be applied to the pavement road surface within such timeframe, and hence, the greater the productivity per roadwork shift. For example, when the road vehicle travels at a speed of one mph (1 mph), the vehicle will travel approximately seventeen inches per second (17″/sec), and the entire adhesive dispensing cycle would then need to be accomplished within approximately two hundred sixty five milliseconds (265 ms). Alternatively, if the road vehicle travels at a speed of four mph (4 mph), the vehicle will travel approximately sixty-eight inches per second (68″/sec), and the entire adhesive dispensing cycle would then need to be accomplished within approximately sixty six milliseconds (66 ms). This rapid cycling of the dispensing of the adhesive composition by means of the applicator dispensing valve permits the applicator road vehicle to move continuously along the road pavement as opposed to being required to stop and start at each marker location in order to dispense the adhesive composition. This reduces wear and tear upon the vehicle while increasing productivity. The valve also needs to dispense the adhesive material with clean and consistent commencement and termination of the dispensing process. This reduces the generation of adhesive material tails, trailing adhesive depositions, or adhesive splatter upon the road pavement surface as the vehicle continues to move forwardly along the road pavement surface. Lastly, the valve must also exhibit good durability and serviceability so as to effectively provide a lengthy service life throughout which millions of pavement markers will be applied to the road pavement surfaces while maintenance or service operations and downtime is minimized.
A need therefore exists in the art for a new and improved plunger-type dispensing valve which can be specifically used for dispensing adhesive compositions onto road pavement surfaces, wherein such dispensing valve will meet the aforenoted criteria and achieve the aforenoted objectives so as to in fact be capable of rapidly affixing pavement markers to road pavement surfaces at predetermined locations along the road pavement surfaces.